The invention relates to a magnetic disk apparatus, and more particularly, a housing structure of a magnetic disk apparatus, which houses therein a plurality of stacked rotating disks for reading and writing information and a rotary actuator supporting a head for reading and writing information on the disks, such that the head is movable between the disks.
With conventional magnetic disk apparatuses, turbulence of an air flowing between disks causes vibration of the disks called “flutter”. When a head is positioned on a disk generating such flutter, the head is degraded in positional accuracy with respect to tracks for reading and writing of information.
As a prior art (1), Japanese Patent Unexamined Publication No. 10-162548 describes a method for forcedly generating an airflow directed to outer peripheries of disks from inner peripheries thereof. As a further prior art (2), there has been proposed a method for reducing a spacing between rotating disks and a housing called a “shroud” which surrounds the disks and is formed concentrically with the disks. Such a shroud is a part of the housing that is disposed in a magnetic disk apparatus to cover components such as magnetic disks, an actuator for positioning of a head, and the like, the shroud surrounding side surfaces of the disks.
An airflow generated around rotating disks includes a primary flow, in which air is dragged by revolution of the disks to flow in a circumferential direction, and a secondary flow, in which air in the vicinity of disk surfaces flows toward outer peripheries of the disks and air between the disks flows toward inner peripheries of the disks. Since the secondary flow involves unstable air turbulence, the prior art (1) is directed to suppressing the occurrence of flutter by generating a forced airflow directed toward the outer peripheries of the disks from the inner peripheries thereof so as to reduce the unstable airflow caused by the secondary flow.
The prior art (2) is directed to reducing flutter by decreasing a gap between disks and a shroud to suppress that incoming and outgoing of air on the top and bottom surfaces of disks, which would be produced in the event of the gap between the disks and the shroud being large, to prevent a pressure difference between the top and bottom surfaces from varying with the passage of time.
As a prior art (3), Japanese Patent Unexamined Publication No. 7-320478 describes a housing structure making use of an airflow circulating in a housing of a magnetic disk apparatus for other purposes than reduction of flutter, and discloses a method for removing dust by means of a filter and cooling an interior of the housing.
If the housing structure of a magnetic disk apparatus is the same, flutter caused by turbulence of an air flowing between disks increases substantially in proportion to a square of a disk radius and the number of revolutions of the disks. Therefore, a housing structure is needed, which reduces flutter having an adverse influence on head positional accuracy, in reduction of track intervals making magnetic disks high in capacity and in increase in the number of revolutions required for achieving high speed.
Provided that the housing structure of a magnetic disk apparatus is the same, the driving power for revolution of disks is substantially proportional to third power of the number of revolutions and fifth power of a disk radius. Accordingly, as with flutter mentioned above, it is necessary to obtain a housing structure that reduces an airflow tending to impose a burden on a rotating driving force, thus reducing a disk driving power in increasing the number of revolutions required for making the magnetic disk apparatus high in speed.
However, the method for forcedly generating an airflow directed toward outer peripheries of disks from inner peripheries thereof offers the following problem. Such method for forcedly generating an airflow directed toward outer peripheries of disks from inner peripheries thereof becomes ineffective because respective arms of a rotary actuator adapted to be inserted between stacked disks block the airflow directed toward the outer peripheries of the disks from the inner peripheries thereof if these arms have a thickness of half or more of an interval between the disks.
Also, the method, in which a gap between disks and a housing called a “shroud” and formed concentric with rotating disks is made small, offers the problem set forth below.
With the method, in which a gap between disks and a housing called a “shroud” and formed concentric with rotating disks is made small, one of the causes for occurrence of flutter can be dissolved because it is possible to suppress fluctuation of pressure difference with the passage of time, which is caused by incoming and outgoing of an airflow on top and bottom surfaces of the disks, even when arms of the rotary actuator are inserted between the disks. However, when the arms are inserted between the disks, they will block the primary airflow, which is dragged by the revolving disks to flow in the circumferential direction. As a result, a high pressure region is generated on an upstream side of the arms while a low pressure region is generated on a downstream side of the arms.
In addition, an air flowing in the circumferential direction on the upstream side of the arms is curved toward the inner peripheries of the disks by the arms to produce a high speed flow directed toward the inner peripheries of the disks. Since such flow directed toward the inner peripheries of the disks tends to return around tip ends of the arms to the outer peripheries of the disks, so it will merge with a flow on the downstream side of the arms to generate turbulence, so that pressure difference between the high pressure on the upstream side of the arms and the low pressure on a downstream side of the arms fluctuates. Such pressure fluctuation causes not only flutter but also a fluctuating force called “wind turbulence” tending to swing the arms. Such swinging of the arms is also responsible for degradation of the head positional accuracy in the magnetic disk apparatus.
Thus, either of the method for forcedly generating an airflow directed toward outer peripheries of disks from inner peripheries thereof, and the method, in which a gap between disks and a shroud is made small, disclosed in the prior art offers a problem that pressure fluctuation generated upon insertion of the arms between the disks cannot be reduced.
Meanwhile, the prior art (3) making use of an airflow circulating in a housing of a magnetic disk apparatus also offers a problem set forth below.
The low pressure region produced on the downstream side of the arms draws in air from outside of the disks. Therefore, when the shroud covers the downstream side of the arms to decrease a gap between the downstream side of the arms and the shroud, high speed airflow enters through the gap into spaces between the disks, thereby causing a significant pressure fluctuation. Presence of a flow passage connecting the upstream and downstream sides of the arms will reduce pressure difference between the upstream and downstream sides of the arms. Thus, pressure loss caused by the insertion of the arms between the disks is reduced, so that the driving power for revolution of the disks is correspondingly reduced.
However, when a flow passage connecting the upstream and downstream sides of the arms is defined in a rotating shaft of the rotary actuator or inside the voice coil motor for driving of the actuator, it inevitably results in a narrow flow passage with many curves, and so causes a considerable pressure fluctuation between disks for the similar reason as mentioned above. The foregoing flow passage is effective in removing dust and cooling the voice coil motor that generates heat. However, it is very likely that wind turbulence and flutter increase when airflow flows through the arm section and an interior of the voice coil motor, which are complex in structure tending to easily develop flow turbulence. In addition, it is unnecessary in a relatively small-sized magnetic disk apparatus to cool the voice coil motor.